In a data recording device, such as a hard disk drive, data is written to circular tracks formed on a disk which is a magnetic recording medium. Therefore, in order to write or read the data, positioning control is necessary for moving a magnetic head to a position on the track. In such a head-positioning mechanism, there are various kinds of measures taken against periodic disturbance caused by various factors.
However, the above disturbance includes, for instance, vibration given to the magnetic disk device whose frequency is hard to specify in advance or the one whose frequency changes with the passage of time. On the other hand, the follow-up control for maintaining the position of the magnetic head relative to a target track is designed to suppress the disturbance in a wide range. As a result, there may be a case where its ability is not enough to suppress disturbance of a specific frequency component.
In recent years, data recording devices such as a hard disk drive have come to be used in various fields including those of portable computers, cellular phones, car-navigation systems, etc. Therefore, a technique to fully suppress the influence of external vibration is desirable.
Japanese Patent Publication No. 2003-109335 (“Patent Document 1”) discloses a method wherein a resonant filter to remove a signal having a specific frequency component is used, and the resonant frequency of the resonant filter is repetitively updated to be gradually close to the frequency of the disturbance so as to remove the disturbance. Moreover, “Frequency Chasing Peak Filter”, M. Kisaka, IEE of Japan Technical Meeting Record, No. IIC-04-70, pg. 19-23 (2004) (“Non-patent document 1”) discloses a technique wherein, when the repetitive updating is performed, such an update-width is determined as the one whose minimum value is set to the square of the position error.
According to the method disclosed by Non-patent document 1, while a convergence rate is increased, a resonant frequency of the resonant filter can be made closer to a target frequency as compared to a case where the update-width is fixed, improving the capability of suppressing disturbance. According to the method disclosed in Non-patent document 1, however, depending on a frequency band to which the resonant frequency belongs, the convergence rate becomes excessively high, resulting in a conversion of the resonant frequency on a frequency away from the target frequency, etc., and desired performance may not be achieved.